The present invention is concerned with improvements in or relating to elastic foamed articles or products composed mainly of inorganic fibers and method for the preparation thereof.
In the prior art relating to the above-mentioned type of inorganic foamed products, there is a well established method which involves stirring of the asbestos fibers in water with the addition of surface active agents to form an asbestos-dispersed slurry entraining and retaining bubbles, and placement of the thus obtained slurry in a desirable mold in the foamed state, followed by drying and, optionally, baking.
The asbestos fibers which generally fall under inorganic fibers can be well dispersed in water with the addition of surface active agents so that they are almost completely opened. This is because they have a thin thickness and a higher degree of softness in comparison with other artificial inorganic fibers such as ceramic fibers encompassing alumina, silica, alumina silicate or zirconic fibers, rock wool, glass fibers, carbon fibers and the like fibers. The asbestos fibers are evenly entangled with each other during the preparation of the above-mentioned inorganic foamed products thanks to their well dispersibility in water, thus giving a fiber-dispersed slurry retaining bubbles in a stable state. Not the least of the problems stemming from the use of asbestos is, however, that it has an adverse influence on the work environment. The asbestos is also disadvantageous in that it possesses rather poor heat resistance; in other words, it merely withstands a temperature up to 500.degree. C.
On the other hand, artificial inorganic fibers such as the aforesaid ceramic fibers, rock wool, glass fibers, carbon fibers and the like fibers offer no appreciable problems in view of the work environment; however, difficulties are encountered in the preparation of a fiber-dispersed slurry retaining bubbles in a stable state. This is because such fibers have a larger thickness and a much lower degree of softness in comparison with the asbestos fibers, and are thus inferior in the dispersibility in water and the water-retaining properties. For this reason, it is impossible to obtain from such fibers the elastic foamed products as discussed above.